1. Field of the Invention
The present invention relates to a method of cleaning a damascene structure of a semiconductor wafer during fabrication of a semiconductor device.
2. Description of the Related Art
In current integrated circuits, several layers of interconnect structures fabricated above a substrate containing active devices are often used. Each interconnect layer is fabricated in an interlayer dielectric (ILD). According to the fabrication of metal interconnects by the metal damascene process, vias are etched in each ILD to make contact with conductors In an underlying layer. A layer of conductive material, such as copper (Cu), is deposited, extending above the surface of the ILD. With chemical mechanical polishing (CMP), the metal surface is then polished down to the underlying ILD surface to thereby produce copper plugs.
After the polishing, the wafer is cleaned. A conventional method of cleaning the metal damascene structure is illustrated in FIG. 5.
In step S1 of FIG. 5, the conventional cleaning method begins with removing particles from surfaces of the wafer. After polishing the wafer, particles are removed in a brushing unit. In the brushing unit, a brush is used to carry out a surface cleaning process with chemical solution in the form of ammonia water. In the same brushing unit, pure water is used to carry out a rinsing process.
Subsequently, the cleaning method proceeds to removing metallic impurities from the surfaces of the wafer. In another brushing unit, metallic impurities are removed. In step S2, in the brushing unit, a brush is used to carry out a surface cleaning process with chemical solution in the form of acid solution. In the same brushing unit, pure water is used to carry out a rinsing process.
After removing metallic impurities, the cleaning method proceeds to inhibiting surface corrosion of the wafer in step S3. In a surface corrosion-inhibiting unit, the surfaces of wafer are coated with chemical solution in the form of solution of 1,2,3-benzotriazol (BTA), which is effective to inhibit corrosion of copper (Cu), subsequently, pure water is used to carry out a rinsing process.
Finally, after the surface corrosion prohibiting process, the cleaning method proceeds to drying the wafer. In step S4, the wafer is rinsed with pure water and then tuned to spin in a spin rinse unit. This spinning motion dries the wafer.
FIG. 6 is a top plan view of a copper plug 3 of a metal damascene structure, which has been cleaned by the conventional cleaning method mentioned above. In FIG. 6, the copper plug 3 embedded in via 2 formed through an ILD 1 has dissolved portions 4 extending outwardly in all directions from the surface of the plug 3. The provision of such portions 4 has made the border between the plug 3 and the circular edge of via 2 of the ILD 1 unclear.
It is the inventor's understanding that the above-mentioned abnormal deformation of surface contour of the plug has occurred due to release of electric charge accumulated within the plug due to rinsing with pure water in a drying unit.
Accordingly, a need remains for a method of cleaning a metal damascene structure of a semiconductor wafer without causing the abnormality of surface contour of the plug.